Method of manufacturing semiconductor device

ABSTRACT

According to one embodiment, the method of manufacturing a semiconductor device includes contacting a film formed on a semiconductor substrate with a rotating polishing pad which is supported on a turntable, and feeding polishing foam to a region of the polishing pad with which the film is contacted, thereby polishing the film. The polishing foam is obtained by turning the aqueous dispersion into a foamy body. The aqueous dispersion includes 0.01-20% by mass of abrasive grain and 0.01-1% by mass of foam forming and retaining agent, all based on a total mass of the aqueous dispersion.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromprior Japanese Patent Application No. 2011-085443, filed Apr. 7, 2011,the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a method ofmanufacturing a semiconductor device.

BACKGROUND

In the manufacture of a semiconductor device, there has been practicedto polish a film deposited on the semiconductor substrate by chemicalmechanical polishing (CMP) using a CMP slurry. The CMP slurry that hasbeen conventionally employed is formed of, for example, a dispersioncontaining abrasive grain wherein pure water is employed as a dispersionmedium. When CMP, a CMP slurry is fed in the vicinity of central portionof a rotating polishing pad. The CMP slurry thus fed spreads to theouter peripheral region of the polishing pad by centrifugal force,thereby the CMP slurry is utilized for the polishing of a film which isbeing contacted with the polishing pad.

All of the CMP slurry that has been fed to the polishing pad is notnecessarily contribute to the polishing of the film to be polished.Since the CMP slurry is low in viscosity and part of the CMP slurry isdischarge outside the polishing pad, the CMP slurry employed in theprior art is not utilized effectively.

If it is possible to retain the CMP slurry on the polishing pad withoutbeing discharged from the polishing pad, the quantity of CMP slurry tobe used can be reduced, thus leading to the improvement of utilizationefficiency of the CMP slurry.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view schematically illustrating a method ofmanufacturing a semiconductor device according to one embodiment;

FIG. 2 is a cross-sectional view schematically illustrating theconstruction of a polishing foam generator;

FIG. 3 is a graph illustrating the relationship between the content of afoam forming and retaining agent and a foam volume reduction ratio;

FIG. 4 is a perspective view schematically illustrating a method ofmanufacturing a semiconductor device according to the prior art;

FIG. 5 is a perspective view schematically illustrating a conventionalmethod of manufacturing a semiconductor device wherein a conventionalslurry is used; and

FIGS. 6A, 6B, and 6C are cross-sectional views illustrating themanufacturing process of STI.

DETAILED DESCRIPTION

In general, according to one embodiment, the method of manufacturing asemiconductor device includes contacting a film formed on thesemiconductor substrate with a rotating polishing pad which is supportedon a turntable; and feeding polishing foam to a region of the polishingpad with which the film is contacted, thereby polishing the film. Thepolishing foam can be obtained by turning the aqueous dispersion into afoamy body. The aqueous dispersion includes 0.01-20% by mass of abrasivegrain and 0.01-1% by mass of foam forming and retaining agent, all basedon a total amount of the aqueous dispersion.

Next, embodiments will be explained with reference to drawings.

A method of manufacturing a semiconductor according to one embodimentwill be explained with reference to FIG. 1. As shown in FIG. 1, asemiconductor substrate 14 which is held on a polishing head 13 to bedriven by a rotating mechanism (not shown) is contacted with a polishingpad 12 supported on a turntable 11 to be driven by another rotatingmechanism (not shown). By feeding polishing foam 15 to a prescribedregion of the polishing pad 12 while rotating the turntable 11 and thepolishing head 13, respectively at a prescribed rotating speed, the film10 deposited on the semiconductor substrate 14 can be polished.

The region of polishing pad 12 to which the polishing foam 15 is fedamong the entire surface of the polishing pad 12 is confined to a regionwith which the semiconductor substrate 14 is contacted. Since thepolishing pad 12 is rotated, it can be said that the region of thepolishing pad 12 to which the polishing foam 15 is fed is confined tothe region corresponding to the orbital tract of the semiconductorsubstrate 14 moving on the polishing pad 12. The polishing foam 15 thathas been fed to the polishing pad 12 enters into an interface betweenthe polishing pad 12 and the film 10 to be polished, thereby polishingthe film 10.

The polishing foam 15 utilized in the polishing of the film 10 to bepolished can be prepared by turning an aqueous dispersion containingabrasive grain and foam forming and retaining agent into a foamy bodyusing a polishing foam generator 16.

The abrasive grain contained in the aqueous dispersion may be optionallyselected depending on the material of the film to be polished. Forexample, if an oxide film such as a thermal oxide film is polished, itis possible to employ cerium oxide, silicon oxide, etc. The content ofthe abrasive grain in the aqueous dispersion is 0.01-20% by mass basedon the total amount of the aqueous dispersion. When the content of theabrasive grain is less than 0.01% by mass, it would be impossible toachieve a practical polishing rate. On the other hand, if the content ofthe abrasive grain is more than 20% by mass, it would be no longerpossible to retain a desired volume of polishing foam and themanufacturing cost would be increased. Preferably, the content of theabrasive grain in the aqueous dispersion is around 0.1-10% by mass basedon the total amount of the aqueous dispersion.

An average particle diameter of the abrasive grain is generally around10-1,000 nm. The average particle diameter of the abrasive grain can bedetermined, for example, by measuring the individual image of each ofabrasive grains which have been obtained by a transmission electronmicroscope or by measuring the specific surface area that has beenobtained by BET method using an automatic fluid type specific surfacearea-measuring, apparatus.

The foam forming and retaining agent makes it possible to turn anaqueous dispersion into a foamy body by passing the aqueous dispersionthrough a polishing foam generator provided with a mesh and also makesit possible to retain the state of foamy body thus formed. However, itis necessary to prevent the foam forming and retaining agent from givingany adverse effects to the polishing of a film to be polished.Therefore, the foam forming and retaining agent is selected taking aboveaffairs into consideration. When an oxide film is polished, it ispossible to employ an anionic surfactant for example as a foam formingand retaining agent. It is also possible to employ ordinary sodiumdodecyl sulfate (SDS) as a foam forming and retaining agent. It isespecially preferable to employ, as a foam forming and retaining agent,alkyl benzene sulfonate and salts of alkyl benzene sulfonate. Among thealkyl benzene sulfonate, it is preferable to employ those having alkylgroup of 8 to 16 carbon atoms. In order to enable the polishing foam toretain its volume while the influence thereof on the polishing speed ofthe film to be polished is taken into consideration, it is morepreferable to employ those having alkyl group of 10 to 14 carbon atoms.In viewpoint of biodegradation, the alkyl group of alkyl benzenesulfonate is preferably of straight chain. As the salts, potassium saltand ammonium are preferable.

Specific examples of alkyl benzene sulfonate and salts of alkyl benzenesulfonate include linear dodecylbenzenesulfonic acid, potassium lineardodecylbenzenesulfonate, ammonium linear dodecylbenzenesulfonate, etc.

The content of the foam forming and retaining agent in the aqueousdispersion is 0.1-10% by mass. If the content of the foam forming andretaining agent is less than 0.1% by mass, it would be impossible tosufficiently secure the effects of enhancing the polishing speed eventhough a certain degree of enhancement can be obtained. Additionally, itwould be impossible to create a desired state of foam. On the otherhand, if the content of the foam forming and retaining agent is morethan 10% by mass, the foam may adhere onto the film to be polished,thereby undesirably decreasing the polishing speed. Incidentally, by theexpression of “a desired state of foam”, it is intended to indicate astate wherein the volume reduction ratio of foam is 5% or less as thefoam is kept standing for 120 seconds at room temperature. It is morepreferable that the volume reduction ratio of foam is 1% or less as thefoam is kept standing for 120 seconds at room temperature. When thecontent of foam forming and retaining agent in the aqueous dispersion isaround 0.5-5% by mass, the aforementioned low volume reduction ratio offoam can be achieved. Details regarding the volume reduction ratio offoam and the formation of foam will be discussed hereinafter.

Depending on circumstances, resinous particle having a nonionicfunctional group on its surface may be co-used. Although this nonionicfunctional group in itself is incapable of acting as a foam-generatingagent, it is possible to derive the effects of suppressing the volumereduction of polishing foam as it is co-used together with theaforementioned foam forming and retaining agent. In this case, it ispossible to reduce the content required of the foam forming andretaining agent. Specific materials of the resinous particle can beselected from, for example, polystyrene, polymethacrylate, etc. Examplesof the nonionic functional group include, for example, carboxyl group,sulfonyl group, etc.

The resinous particle having a nonionic functional group on its surfacecan be obtained according to the preparation method described, forexample, in Example 4 of JP-A 2000-204353 (KOKAI).

The aqueous dispersion can be obtained by adding a predeterminedquantity of abrasive grain and of foam forming and retaining agent towater. As for the water, it is possible to employ pure water, forexample.

The aqueous dispersion thus prepared contains a foam forming andretaining agent and abrasive grain and can be turned into a foamy bodyby passing it through a polishing foam generator. The polishing foamgenerator 16 is constructed, for example, as shown in FIG. 2. A mixingchamber 20 is provided inside a cylindrical resinous cylinder block 17and communicated with a feeding passageway 18. The aqueous dispersioncontaining a foam forming and retaining agent and abrasive grain can befed, via the feeding passageway 18, into the mixing chamber 20 andaccommodated therein.

By supplying air from the feeding passageway 18 to the interior of themixing chamber 20, the aqueous dispersion is agitated and then allowedto pass through a mesh 19, thereby enabling the aqueous dispersion toturn into a polishing foam. The polishing foam is then discharged from adischarge opening 21 of the polishing foam generator 16. With respect tothe aperture of mesh 19, as long as it is around 100-500 meshes, it ispossible to create a desired state of foam. With respect to thematerials of mesh 19, there is not any particular limitation and hencethe mesh 19 may be formed of nylon, polyester, polyethylene, etc.

The supply flow rate of air can be regulated by an electropneumaticregulator. By blowing air into the aqueous dispersion containingprescribed quantities of a foam forming and retaining agent and abrasivegrain under appropriate conditions, a foamy body can be obtained in adesired state. In order to obtain a foamy body in a desired state, thetemperature of the aqueous dispersion is preferably within the range of18-30° C. The air is desirably supplied in such a manner that the volumeof air becomes 2-10 times larger than the volume of the aqueousdispersion. Further, it is also effective, in order to obtain foam ofdesirable state, to supply air through a filter so as to minimize theimpurities in the air.

The polishing foam created in this manner by the polishing foamgenerator is featured in that the volume reduction ratio after 120seconds is 5% or less. It is more preferable that the volume reductionratio after 120 seconds is 1% or less.

The volume reduction ratio can be defined as follows. First of all, bythe aforementioned polishing foam generator, an aqueous dispersion isturned into a foamy body, which is then accommodated in a graduatedcylinder to determine the initial volume (V₀) of the foamy body. Thefoamy body thus determined is left standing for 120 seconds under theconditions of windless atmosphere and room temperature and then thevolume (V₁₂₀) after 120 seconds is measured. Thus, volume reductionratio of the foamy body can be obtained from {100×(V₀−V₁₂₀)/V₀}.

In the ordinary polishing process, the time required for polishing thefilm to be polished and being deposited on the semiconductor substrateis 120 seconds or less. As long as the polishing foam obtained as afoamy body from an aqueous dispersion can be kept in a desirable state,the polishing foam stays on the polishing pad, thus contributing to thepolishing of the film to be polished. Since the polishing foam isreliably utilized for the polishing of the film to be polished, it ispossible to secure a practical polishing speed. Moreover, the polishingfoam applied to the polishing pad can be prevented from being dischargedfrom the polishing pad even if the polishing foam is subjected to acentrifugal force (the rotational speed of the turntable is 10-150 rpmin general), thus making it possible to enhance the utilizationefficiency of the polishing foam.

The state of the polishing foam can be assessed by the value of foamvolume reduction ratio. It has been found out by the present inventorsthat as long as the foam volume reduction ratio after 120 seconds is 5%or less, it is possible to obtain desired effects of polishing foam.

Examples

Next, specific examples of the method of manufacturing a semiconductordevice will be explained.

Embodiment 1

Abrasive grain was added to a dispersion medium to obtain an aqueousdispersion containing 0.5% by mass of the abrasive grain. Cerium oxidehaving an average particle diameter of 0.1 μm was employed as theabrasive grain and pure water was employed as a dispersion medium. Theaqueous dispersion thus obtained was employed as Sample 1. This Sample 1corresponds to a CMP slurry which has been conventionally used.

To this Sample 1 was added predetermined quantities of potassium lineardodecylbenzenesulfonate as a foam forming and retaining agent to obtainSamples 2-8. The amount of potassium linear dodecylbenzenesulfonate wereregulated so that these samples could be formed respectively aspolishing foam and that the foam volume reduction ratio thereof afterstanding for 120 seconds at room temperature would be confinedrespectively to a predetermined value. In order to create the polishingfoam, a polishing foam generator constructed as shown in FIG. 2 wasemployed. The capacity of the mixing chamber 20 was around CO cc and a300-mesh polyethylene mesh was employed as the mesh 19. The diameter ofthe discharge opening 21 was about 5 mm. Air was supplied controllingthe original pressure thereof to 0.5 MPa by an electropneumaticregulator.

The foam volume reduction ratio and the content of each of the foamforming and retaining agents are summarized in the following Table 1.Further, the relationship between the content of foam forming andretaining agent and the foam volume reduction ratio was plotted as shownin the graph of FIG. 3.

TABLE 1 Foam Foam forming Sample volume-reduction and retaining No.ratio (%) agent (mass %) 2 10 0.01 3 6 0.05 4 5 0.1 5 3 1 6 0.7 5 7 0.510 8 0.5 15

Further, a sample exhibiting a volume reduction ratio of 0.5% wasobtained as Sample 9. This sample 9 contained resinous grain having anonionic surface functional group. The content of the resinous grain inthe Sample 9 was about 0.1% by mass. This surface functional group wascarboxyl group and the resinous grain was about 50 nm in averageparticle diameter and formed of styrene/methacryl copolymer.

Using Sample 1, a thermal oxide film deposited on the semiconductorsubstrate was polished. This thermal oxide film was 300 nm in thicknessand the diameter of the semiconductor substrate was 200 mm. Whenpolishing the thermal oxide film, the polishing head 13 holding thesemiconductor substrate 14 was forced to contact with the polishing pad12 at a polishing load of 300 hPa while driving the turntable 11 havingthe polishing pad 12 attached thereto to rotate at rotational speed of100 rpm as shown in FIG. 4. The rotational speed of the polishing head13 was 103 rpm. By following the conventional supply method, Sample 1constituting the slurry 25 was fed from the slurry supply nozzle 26 to acentral region of the polishing pad 12. The flow rate of the slurry 25was set to 100 cc/min. This flow rate corresponds to the ordinary flowrate of slurry which has been conventionally employed.

The slurry 25 applied dropwise to a central region of the polishing pad12 spread toward the peripheral region of the polishing pad due to thecentrifugal force, thereby the slurry 25 is utilized for the polishingof the thermal oxide film. The polishing pad employed herein was formedof IC1000 (Rodel Co., Ltd.). The polishing was performed for 60 seconds.

The thermal oxide film was polished under the same conditions asdescribed above excepting that the flow rate of the slurry 25 to be fedfrom the slurry supply nozzle 26 was changed to 50 cc/min and to 25cc/min. In this case, the polishing speed was estimated from thequantity shaved from the thermal oxide film. The flow rate of Sample 1and the polishing speed are summarized in the following Table 2.

TABLE 2 Flow rate Polishing speed (cc/min) (nm/min) 100 158 50 143 25102

As shown in above Table 2, when the flow rate of slurry was 100 cc/min,the polishing speed was 158 nm/min, thus indicating that it was possibleto polish the thermal oxide film at a practical speed. When the followrate was decreased, the polishing speed was also decreased. When thefollow rate was 25 cc/min, the polishing speed was decreased to 102nm/min. Since the polishing speed of the thermal oxide film is at leastrequired to be 150 nm/min or more, above-mentioned polishing speed isnot practical.

Then, using the polishing foam generator 16 shown in FIG. 2, the samplesNos. 1-9 were respectively fed only to the region of the polishing pad12 which corresponds to the orbital tract of the semiconductorsubstrate. In every case, the amount of the sample thus applied was 25cc. The polishing of the same thermal oxide film as described above wasperformed under the same conditions excepting the quantity of thesample.

When the samples Nos. 2-9 were respectively feed as described above, thepolishing foam 15 was placed at a predetermined region of the polishingpad 12 as shown in FIG. 1. The polishing foam 15 placed on the polishingpad 12 by each of samples of Nos. 4-9 was substantially incapable ofexhibiting fluidity, thus enabling the polishing foam 15 to remain atthe predetermined region of the polishing pad 12. It was assumed thatthe polishing foam 15 thus placed contributed to the polishing of thefilm throughout the entire period of polishing.

The polishing foam 15 created by each of samples of Nos. 2 and 3 waseasily fluidized and hence was incapable of being stably kept in place.The sample of No. 1 was not foamy and a portion 27 thereof wasdischarged out of the polishing pad as shown in FIG. 5.

In the same manner as describe above, the polishing speed was estimatedfrom the quantity shaved from the thermal oxide film. The polishingspeed each of these samples is summarized in the following Table 3.

TABLE 3 Sample Polishing speed No. (nm/min) 1 39 2 115 3 120 4 169 5 1616 157 7 153 8 135 9 166

Since Sample 1 was an aqueous dispersion, even if it was fed, using apolishing foam generator, to the region of the polishing pad whichcorresponds to the orbital tract of the semiconductor substrate, Sample1 was incapable of being stably kept in place on the polishing pad.Since Sample 1 thus fed was discharged out of the polishing pad due tocentrifugal force, the degree of Sample 1 that contributes to thepolishing of the film was extremely minimized. Because of this, thepolishing speed of the thermal oxide film was as very low as 39 nm/min.When slurry formed of an aqueous dispersion is employed, it isimpossible to polish the film at the practical polishing speed unlessthe slurry is fed according to the conventional method.

In the cases of Samples 2 and 3, although they were respectively turnedinto a foamy body, the polishing speed thereof was as low as 120 nm/minor less, thus indicating insufficient polishing speed. The reason forthis is assumed to be attributed to the fact that since the volumereduction ratio of these foamy bodies was too large, it was impossibleto enable them to contribute to the polishing of the film to bepolished.

The polishing speed in the cases of Samples 4-7 and 9 was all not lessthan the value that was obtained when the Sample 1 was supplied at aflow rate of 100 cc/min. Since the amount of feeding these samples wasrespectively 25 cc, it was possible to obtain a practical polishingspeed even when the feeding amount of these samples was as small as 1/4of Sample 1.

In the case of Sample 8, although it was possible to keep the volume offoam, the polishing speed was as low as 135 nm/min. The reason for thiswas assumed to be attributed to the fact that since the content of thefoam forming and retaining agent was as large as 15% by mass, the foamadhered to the film to be polished, thereby decreasing the polishingspeed.

It was found out that when the method of this embodiment was adoptedemploying a polishing foam exhibiting a foam volume reduction ratio of5% or less, it was possible to polish a film to be polished at apractical polishing speed even if the quantity of slurry to be used wasreduced.

Embodiment 2

The method of manufacturing shallow trench isolation (STI) will beexplained with reference to FIGS. 6A to 6C.

First of all, a semiconductor substrate 30 having a silicon nitride film31 deposited thereon and provided with an STI pattern B as shown in FIG.6A was prepared. The silicon nitride film 31 acts as a stopper film andthe film thickness thereof is 50 nm for example. A silicon oxide filmfor example may be interposed between the semiconductor substrate 30 andthe silicon nitride film 31. Using the silicon oxide film as an etchingmask, the semiconductor substrate 30 is worked together with the siliconnitride film 31 to form the STI pattern B.

The width and intervals of this STI pattern B are both 1 μm (line/space:1/1 μm). Further, the depth of this STI pattern B is 200 nm for example.

As shown in FIG. 6B, a silicon oxide film 32 is deposited on the siliconnitride film 31 by a high-density plasma CVD (HDP-CVD) method forexample. The film thickness of the silicon oxide film 32 is 280 nm andthis silicon oxide film 32 is formed all over the surface of siliconnitride film 31 including the regions other than the STI pattern B.

Then, the surface of silicon oxide film 32 is entirely subjected to CMPto remove the silicon oxide film 32 existing outside the STI pattern Bas shown in FIG. 6C. As a result, the silicon oxide film 32 is buried inthe STI pattern B and the surface of silicon nitride film 31 is exposedat the regions other than the STI pattern B.

On the occasion of performing the CMP, the silicon oxide film ispolished at first under the conditions conventionally employed. Morespecifically, the aforementioned Sample 1 is fed at a flow rate of 100cc/min and the polishing is performed under the same conditions asdescribed above. The polishing speed is 158 nm/min.

Further, using aforementioned Sample 5, the silicon oxide film ispolished under the same conditions as described above. Namely, using apolishing foam generator, 25 cc of Sample 5 is turned into a foamy body,which is then applied only to the region of polishing pad correspondingto the orbital tract of the semiconductor substrate. The polishing speedis 161 nm/min.

The time required for exposing the surface of silicon nitride film 31,the depth of dishing on the surface of silicon oxide film 32 that wasleft remain in the STI pattern B and the number of defectives wereinvestigated, the results being summarized in the following Table 4. Ifthe depth of dishing is not more than 30 nm, it is considered asacceptable.

TABLE 4 Sample Polishing Dishing Number of No. time (sec) (nm)defectives 1 95 15 23 5 92 18 20

Above Table 4 indicates that, as in the case of Embodiment 1, even ifthe quantity of slurry used was reduced to 1/4 of Sample 1, it waspossible to obtain almost the same CMP performance.

Embodiment 3

Silicon oxide having an average particle diameter of 25 nm is preparedas abrasive grain. This silicon oxide is added to pure water employed asa solvent to obtain an aqueous dispersion containing 10% by mass ofsilicon oxide. The aqueous dispersion thus obtained is used as Sample10. This Sample 10 corresponds to a CMP slurry which has beenconventionally used.

To this Sample 10 is added predetermined amount of ammonium lineardodecylbenzenesulfonate as a foam forming and retaining agent to obtainSample 11 as polishing foam. The foam volume reduction ratio of thisSample 11 after standing for 120 seconds at room temperature is 4%.

In the employment of Sample 10, the polishing of a silicon oxide film isperformed under the same conventional conditions as described inEmbodiment 1. More specifically, Sample 10 is fed at a flow rate of 10cc/min and the polishing was performed under the same conditions asdescribed above. The polishing speed is 108 nm/min.

On the other hand, in the employment of Sample 11, 25 cc of Sample 5 isturned into a foamy body using a polishing foam generator and thenapplied only to the region of polishing pad corresponding to the orbitaltract of the semiconductor substrate. The polishing speed is 121 nm/min.

When compared with cerium oxide, although the polishing speed to beobtained using silicon oxide was decreased, the polishing speed was notlowered even if the flow rate thereof was reduced to 1/4. It wasconfirmed that even if silicon oxide was employed as abrasive grain, itwas possible to obtain almost the same effects as in the case of ceriumoxide.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

1.-17. (canceled)
 18. A polishing apparatus comprising: a rotatableturntable; a polishing head configured to hold a semiconductor substratehaving a film formed thereon and contact the film with a polishing padsupported on the rotatable turntable; and a polishing foam generatorconfigured to accommodate an aqueous dispersion comprising abrasivegrain and a foam forming and retaining agent and discharge, through amesh, the aqueous dispersion as a foamy body to feed the polishing foamto a region of a polishing pad with which the film is contacted.
 19. Theapparatus according to claim 18, wherein the mesh is formed of amaterial selected from the group consisting of nylon, polyester andpolyethylene.
 20. (canceled)
 21. The apparatus according to claim 18,wherein an aperture of the mesh is 100-500 meshes.
 22. The apparatusaccording to claim 18, wherein the polishing foam generator isconstituted by a cylinder unit having a chamber configured toaccommodate the aqueous dispersion.
 23. The apparatus according to claim22, wherein the cylinder unit is formed of a resin.
 24. The apparatusaccording to claim 22, wherein the cylinder unit comprises a passagewaycommunicated with the chamber, the aqueous dispersion being fed via thepassageway.
 25. The apparatus according to claim 24, wherein thepassageway is configured to supply the chamber with air in addition tothe aqueous dispersion.
 26. The apparatus according to claim 25, whereinthe polishing foam generator comprises a regulator configured toregulate a flow rate of the air supplied to the chamber.